A growing body of work during the past several years indicates that small neutral amino acids, glycine being the prototype, play critical roles in maintaining structural integrity of several types of kidney tubule cells from a variety of species. Recently, we have found evidence for similar, novel actions of specific amino acids to potently protect human umbilical vein endothelial cells from lytic plasma membrane damage produced by either a calcium ionophore or hydrogen peroxide. The exogenous amino acids are effective at physiological concentrations and serve to replace free intracellular amino acids that are rapidly lost during injury. Based on the concentrations of amino acids with protective effects in common tissue culture media, this has been an unrecognized variable in virtually all prior studies of endothelial cell injury in vitro. Because of their involvement in multiorgan pathophysiology and the possibility that they are even more prone to depletion of the relevant amino acids than tubule cells, endothelial cells may be prominent sites for expression and modulation of this phenomenon. As the next steps to assess this, it is of importance to know what types of endothelial cells behave in this fashion, what forms of damage can be modulated, and whether Ca2+-induced injury is the main target. The proposed studies will test the general hypothesis that variations of availability of specific small neutral amino acids critically contribute to endothelial cell susceptibility to damage by mediators of inflammatory injury. We will address the following questions: 1) What types of endothelial cells other than human umbilical vein cells exhibit amino acid effects? 2) What additional forms of in vitro injury are amenable to modification by amino acids, with particular emphasis on application to the inflammatory injury which is likely to be most relevant to disease states involving endothelial cells in vivo? 3) Which prelethal metabolic events and sublethal forms of injury are subject to modification by amino acids? 4) Does the common mechanism for cytoprotection by glycine and related amino acids of endothelial cells involve interruption of injurious events induced by increased cytosolic free Ca2+? 5) How are intracellular levels of protective amino acids in endothelial cells regulated?